Fluidized distillation of oil-shale



June 23, 1953 J. w, CARR, JR., ET AL 2,643,219

FLUIDIZED DISTILLATION OF OIL-SHALE Filed June 21, 1949 4 Sheets-Sheet l (fiance or .SHALE PAR rive/.5 SIZE WITH TIME SHALE FEED .s'rnn'rso AT RUN noun 73 .SHALE FEED STOPPED HT Run HOUR I47 7010-20 0 0-K: M/c/zom MICRONS 5% QGMKROME 1 20-80 351 455517 351 1551! MICRO/VS J. w. CARR, JR., ET AL 2,643,219 FLUIIDIZED DISTILLATION OF OIL-SHALE 4 Sheets-Sheet 2 AVE/2 AGE DISENGAG/NG HEIGHT --//.0 F7.

0 30% 0-20 M0 MA 75 2 /AL 0 5% 0 -20 MUM/1 7512 [AL E/VTRA l/VMENT OF SPENT SHALE /2" C/RCULA TOE June 23, 1953 Filed June 21, 1949 Q x W/ [W Y n c O L m D E B m m F m w 5 June 23, 1953 J. W. CARR, JR, ET AL FLUIDIZED DISTILLATION OF OIL-SHALE 4 Sheets-Sheet 5 Filed June 21, 1949 SHALE DR UM .SHALE OUTLET JPENT 1 t r g 5 6 m 1 t G 7 I 9 a 5 6 5 s2 2. M t .14. I L 5 Y 3 M "M 7 a a x z o v. 3 7 cH All 3 .L W2 l s 2 F s .i 'm fi m. V 6 an R 5 o 2 A E 9 T M M K s o i/K MW 4 June 1953 J. w. CARR, JR., ET AL 2,643,219

FLUIDIZED DISTILLATION OF OIL-SHALE Filed June 21, 1949 4 Sheets-Sheet 4 TO QYCLOIYES T STUFF HG BOX 2 W SLIDING SECTION OF ADJUSTABLE TAKE-OFF PIPE STUFF/AVG BOX B ku/Ne VESSEL Top HEAD Patented June 23, 1953 UNITED STATES PATENT OFFICE 2,642,219 FLUIDIZED DISTILLATION OF OIL-SHALE Application June 21, 1949, Serial No. 100,492

6 Claims. (01. 202-14) The present invention relates to the art of distilling carbonaceous solids, such as oil-bearing minerals including oil shale, oil sands, tar sands, and the like, maintained in the form of subdivided particles in a highly turbulent state fluidized by upwardly flowing gases to resemble a boiling liquid, wherein the heat required for distillation is supplied by burning spent solid distillation residue in a separate combustion zone and circulating hot solid combustion residue to the distillation zone. More particularly, the present invention relates to improved means for controlling the particle size of the fluidized solids masses and circulating solids within desirable ranges. The invention will be fully explained hereinafter with reference to the accompanying drawing in which Figures 1 to 3 are graphical illustrations of effects obtainable in accordance with the invention;

Figure 4 is a semi-diagrammatical illustration of a system suitable to carry out the process of the invention; and

Figure 5 is a similar illustration of a specific embodiment of the invention.

Prior to the present invention, it has been proposed to carry out the pyrolytic treatment or distillation of oil shale in the form of subdivided solids ranging in particle size from a fine powder up to rather large aggregates of, say, about /4 inch diameter in a highly turbulent fluidized state while supplying the heat required by this reaction as sensible heat of hot solid combustion residue in the manner indicated above. The principal problem encountered in this type of operation arises as the result of a strong tendency of the shale to disintegrate rapidly in the course of the pyrolytic treatment to particles of extremely small size which complicate and frequently even provent proper fluidization and solids circulation. The maintenance of proper fluidization conditions normally requires a. relatively low percentage, say, less than about 55% of particle sizes below 20 microns diameter. However, it is desirable in commercial operation to maintain the fines concentration between 20 and because relatively high apparent densities of the circulating solids permit the use of lower standpipes and a lower surface area of the particles reduces undesirable oil adsorption on the circulating solids, in the retort. The oil shale powder formed during distillation has a particle size generally below 40 microns and mostly below 20 microns, independent of the particle size of the raw shale. In addition, spent shale.

2 that is the solid residue from the distillation stage, has a very high attrition rate amounting to about 10-20 times the attrition rate of other fluidizable siliceous material, such as conventional fluid cracking catalyst.

These shale characteristics are illustrated in Figure l which summarizes in graphical form the disintegration and attrition of retorted shale, that is solid residue from the distillation stage, in pilot plant operation. The experiments yielding these data were carried out in a two-vessel fluid retorting system operating at the following conditions:

Retort 900-940 F. Burner l000-1080 F. Feed rate 800 #/hr. Burner overhead losses (no recovery system) 350-500lbs./hr. Retort velocity 1.0 ft./sec. Burner velocity 1.5-2.0 ft./sec. Circulation rate 180-210 #/min.

Before fresh shale was charged, the system was brought up to temperatures using a fluidized circulating charge of spent silica-alumina cracking catalyst having a particle size distribution as follows:

Size: Weight, per cent 0-10 microns 4 10-20 microns 5 20-80 microns 71 80-400 microns 20 The charge was heated by circulation through a gas fired heat exchanger until a temperature of 650 F. was reached at which point torch oil was injected into the burner to raise the charge to distillation temperature. Thereafter, the system was placed on steam using raw shale containing only 2% material less than 80 microns and passing three mesh.

The data presented in Figure 1 show rapid disintegration of the fresh shale within about 24 hours after the raw shale was first added which took place hours from the time heating of the spent catalyst charge was begun. It will be appreciated that this rate of disintegration, if unchecked, causes a rapid accumulation of shale fines in a system of the two-vessel type described above wherein the shale is maintained for a considerable length of time at and above distillation temperatures and continuously subjected to attrition in the turbulent fluidized beds as well as during circulation between the combustion and distillation zones. As this fines accumulation proceeds, fiuidization becomes irregular and all solids are eventually carried overhead by the fluidizing gases. The present invention is designed to overcome this difiiculty.

It is, therefore, the principal object of the present invention to provide improved means for controlling the particle size of oil shale undergoing distillation in a fluid-type distillation system wherein the shale is continuously circulated between a distillation zone and a heat-generating combustion zone. Other and more specific objects and advantages will appear from the description of the invention given below wherein reference will be made to the accompanying drawing.

In accordance with the present invention, excessive accumulation of shale fines is prevented by the selective removal of the shale fines of undesirably small particle size from the fluidized shale beds with the aid of the elutriating effect of the upwardly flowing fluidizing gases. In accordance with the preferred embodiment of the invention, this elutriation of fines takes place predominantly or exclusively in the combustion zone. In this manner, losses of oil products and fuel which are associated with the shale fines in the distillation zone may be substantially reduced. As a further result, an equilibrium fines concentration in the circulating solids is established.

This is illustrated by the curves of Figure 1 wherein the pilot plant operating at the conditions described and in accordance with the present invention reached equilibrium particle size of 55% -20 microns particles within about 30 hours. It will be understood, of course, that a lower fines equilibrium may be attained when the linear superficial gas velocity in the burner is increased above the 2.0 ft. per second specified above as an upper limit, provided complete bed blow-out is prevented.

It has also been found, that the spent shale, even after it has been burned in the combustion stage, includes a substantial proportion of, say, about 12 to 28% of relatively large particles of about 420 to 7,000 microns diameter which are highly attrition resistant. Accumulation of this coarse material when accompanied by the removal of fines in accordance with the invention will lead to an undesirable particle size distribution toward excessively large particle sizes and thus to fluidization difliculties. This may be avoided in accordance with a preferred embodiment of the invention by a controlled and selective, substantially simultaneous removal of undesirably small shale fines overhead and of undesirably large particles downwardly, from a fluidized shale bed, under the elutriating influence of the fluidizing gases.

Whenever the particle size controls described above are found to be inadequate to establish proper fluidization conditions, particularly as a result of a deficiency in particles of intermediate size ranges, such as about 60-200 microns diameters, the invention provides for the addition of extraneous material of such particle size in proportions adequate to establish the proper particle size distribution. Concentrations of 25 to 50% of particles of this intermediate size are normally desirable. While any inert material having a specific gravity in the neighborhood of that of spent shale, such as sand, clay, etc., may be used for this purpose, greatest advantages are secured when conventional cracking catalysts, such as various natural or artificial clays, suitable composites of silica, alumina and/ or magnesia, or

the like, are employed as the extraneous material Of intermediate particle size. In this manner, the invention affords a substantial improvement in the yield and quality of the gasoline range hydrocarbons produced, in addition to the stabilization of the fluidity characteristics in the reaction zones.

Extensive research work has demonstrated that shale fluidization is satisfactory at superficial linear gas velocities of about 0.3-3 ft. per second, provided that the concentration of fines of 0-20 microns diameter does not exceed 2550% of the total. Segregation of the fines from the coarse material in the fluidized bed occurs in that portion of the velocity range just indicated which lies below 1.2 ft. per second but only when the fines content is maintained at less than 25% of 0-20 micron particle size. This segregation occurs without any detrimental effect on the fluidity characteristics of the fine portion of the fluidized bed.

Selective elutriation of the finer particles from the bed occurs as is illustrated in Figure 2 which shows a diagram wherein the shale entrainment rate expressed as pounds of shale per cu. ft. of gas is plotted against the superficial linear velocity of the fluidizing gas in the fluidized bed, for the fluid shale beds containing 5% (Curve I) and 30% (Curve II) of fines of 0-20 microns diameter, respectively. The initial and final particle size distribution of the solids tested was as follows:

TABLE I Shale entrainment studies Curve 'II Curve I let Series 2nd Series 3rd Series Initial Final Initial Final Initial Final '0-20 Microns... 1 26. 5 30. 5 28. 5 33.0 2. 5 8.0 20-40 hlicronsu 5. 0 4.0 4.0 0.5 1.0 40-80 lvlicrons. 8. 5 4. 5 4.0 .l. 5 2. 5 -100 Microns 2. 0 1.0 1.0 1.5 0. 5 On Mosh. -4. 0 14.0 9. 0 11.5 9. 0 On 80 Mesh. 13.0 17.0 14.0 19.0 14.5 On 35 Mcsh. 12.5 13.0 11.0 17.5 15.5 On 20 lHesh. 17.0 13. 5 10.0 39.0 40. 5 0118 Mcsh 7.5 4.5 8.0 7.0 8.5 On3Mcsl1. 0 0 0 0 0 No sample available; fines content estimated, based on attrition rate shown during second series.

The tests were carried out as follows:

The spent shale used in these tests was obtained by previous operation of a single vessel fluid retorting pilot plant. Raw shale of approximately 4 inch maximum particle size was fed to the top of the fluid bed and the coarser spent shale was withdrawn from the bottom of the bed. Entrained fines, called spent shale fines, were collected on filters from the gas stream leaving the retort. The bed was fluidized by steam containing sufficient air to burn residual carbon on the shale and provide heat necessary for the distillation of the oil. The range of operating conditions over which the spent shale used in these tests was collected are as follows:

Fluidizing velocities 0.73 to 3.5 ft./sec.

Retort temperatures, "F 920 to 1040 F.

Shale feed rate 30 to 1001bs./hr.

Oil content of shale 48 to 42 gal/ton Nominal holding time 18 to 53 minutes (inventory feed rate) Entrainment tests were carried out in a 12 inch glass vessel with the two returning cyclones dis connected and returning to separate collecting cans. The unit was charged with known weights of a mixture of coarse and fine spent shales obtained as described above and operated at a given gas velocity for a short period. The total overhead collections were collected, weighed and sampled for particle size determinations. With the weight of material carried overhead and the gas velocity, the entrainment loss in pounds per cubic foot of gas could be calculated. Three separate charges were run at each of several velocities with the overhead collections being returned to the fluidized bed prior to each change of velocity. The first two were mixed to contain 30% -20 micron particle size and were run for confirmation of the data. The third test Was run with 0-20 micron particle size to determine the efiect of particle size. The total particle sizes of the three materials tested are listed in Table I. The curves of Figure 2 show that there is a critical gas velocity of about 1.5 ft. per second above which carry-over of entrained solids increases rapidly as the flow velocity is increased. On the basis of these experimental results the invention provides for maintaining superficial linear fluidizing gas velocities of about 1.5-3'ft. per second, particularly in the combustion section of a two-vessel shale distillation system.

The flow velocity within this range may be chosen in such a manner that a fines removal rate is established which approaches that of the fresh shale feed to the distillation zone. However, it is also possible so to control the velocity of the fluidizing gas above about 1.5 ft. per second that the fines concentration in the fluid bedis maintained at less than and that segregation of coarse material takes place in the lower portions of the bed, effecting a particle size control entirely independent of the fresh feed and solids circulation rates. Systems suitable for this purpose will be described below with reference to Figures 4 and 5 of the drawing.

As pointed out above, the particle size distribution may be further improved by the addition of extraneous solids of intermediate particle size whenever the fluid bed is deficient in such particle sizes. When operating at the flow velocities of the invention this material of intermediate size will be retained in the system with little loss by entrainment. This is borne out by the I data presented in Figure 3 in which the fines concentration (010 microns material in Curve I, 0-20 microns material in Curve II) in the total entrainment is plotted against linear superficial velocity of the fluidizing gas in the fluidized bed. It will be seen from Figure 3 that even at high total entrainment rates corresponding to the higher gas velocities, the proportion of material of more than 20 microns particle size in the total entrainment is relatively small amounting to less than about Loss of material of intermediate size with the coarse material withdrawn from the lower portions of the bed may b minimized by an effective segregation within the bed as will appear more clearly hereinafter.

The overhead removal of fines, particularly from the combustion zone, in accordance with the present invention may be made still moreselective by introducing at least a substantial portion of the spent shale withdrawn from the distillation zone into an upper portion of the combustion zone, preferably above or just below the dense phase interface. It has been found that the selectivity toward fines entrainment, preferentially over the entrainment of coarser materials, increases as the carbon content on the solids increases. The carbon content of the spent shale is highest before it is subjected to combustion. Therefore, when the spent shale is introduced into the top of the burner bed, the highcarbon fines are selectively elutriated as they enter the bed and removed from the bed in a gas which is essentially a flue gas poor in oxygen, produced in the lower portions of the burner bed, so that these fines are not burned, but retain their high carbon content and with it their high gas buoyancy. The coarser particles, on the other hand, entering the top of the burner bed pass downward into the body of the fluidized burner bed and are burned substantially free of fixed carbon before they are returned to the distillation zone for heat supply. The oxygen in the combustion-supporting gas supplied to the bottom of the burner is burned to a low concentration to form the flue gas just mentioned.

If the distillation zone or retort is located above the combustion zone or burner, the retorted shale particles may be discharged directly into the top of the burner through a conventional standpipe provided with a slide valve. The combustion-supporting gas is supplied to the bottom of the burner where the burnt particles are withdrawn for recycling to the retort. If the retort is located below the burner or at the same level, a part of the retorted solids may be circulated to the top of the burner, preferably suspended in flue gas or steam, and another, preferably larger, portion may be introduced at the bottom of the burner preferably with the entering stream of combustion-supporting gas. If desired, mixing of the incomin high-carbon fines with the rest of the fluidized bed may be reduced by restricting free circulation of fluidized solids between the upper and lower portions of the bed. This may be accomplished in any manner known per se, for example by arranging a non-fluidizable packing or a perforated plate with downcomer in the upper portion of the fluidized bed.

It may also be desirable in certain cases to introduce the fresh shale into the retort at a point above or preferably just below the interface of the dense solids phase. In this manner, at least a portion of the retorted oil vapors may be liberated in the upper portion of the bed and withdrawn therefrom without rising through a deep bed of highly adsorptive fine shale particles by which it may be adsorbed and carried to the burner, which is highly undesrable. Simultaneously, overhead entrainment of shale fines from the retort is reduced in this manner, because by preventing oil adsorption as described the carbon content and with it the gas buoyancy of the shale fines are kept low. Finally, flash vaporization of oil and water from the fresh shale which frequently leads to violent surges in the dense bed with spurts of shale fines thrown into the dispersed phase, may be avoided. All these effects cooperate substantially to improve operation and liquid yields of the process.

Having thus described its objects and general nature the invention will be best understood from the following more detailed description wherein reference will be made to Figures 4 and 5 of the drawing.

Referring now to Figure 4 the system illustrated therein essentially comprises a distillation chamber or retort l0 and a combustion chamber or burner 40, the functions and cooperation of which will be forthwith described using as an example the distillation of an oil shale containing about 0.5 13131. of distillable oil constituents. per

ton. It should be-understood, however, that other:

oil bearing minerals may be treated in a sub.- stantially analogous manner.

In operation, feed hopper l contains fresh oil shale crushed to a .particle size of about 3 to 200 mesh. A suitable particle size distribution ofthe fresh shale may be about as followsr.

Mesh size:

On 4 mesh c The shalein hopper! may-be preheatedyto'any desired temperature of, say, about 300-500 F. and simultaneously dried-in any manner; known per se, for example in heat exchange with hot product orflue gases. Fresh shale flows from hopper-l downwardly throughline 5. The-solids flow may be controlled-by suitable means, such as a screw conveyor, star feeder, reciprocating slide valve, etc. The fresh shale discharges into an upper or intermediate portion of retort l0.

Simultaneously, a gas such as product tail gas, steam, CO2 or'other inert gas containing suspended hot solids supplied from burner 40'as will appear more clearly hereinafter, is fed to the lowerportion of retort from line 12 through a' suitable distributing device, such as a grid or inverted conel4. Retort i0 is so designed that at the prevailing conditions of solids circulation and carrier gas rates the superficial linear velocity of the gas in retort I0. is about 1.2 to 1.5 ft. per second. Sufficient hot, solids from burner 40' are supplied with the gas throughline l2 and cone [4 to maintain within retort 10 a solids temperature of about 900-1200 preferably about 950"- 1100 F., suitable for shaledistillation. At the conditions specified, a fluidized highly turbulent relatively dense shale-bed M10 having a welldefined upper interface L10 is formed in retort {Hand distillation takes place. As a result, the fresh shale disintegrates rapidly to form about 20-40%' of fines having a particle size of less than 20 However, in the example illustrated by Figure 4, extraneous solids having a particle size of about 60-200 microns are added to the system from hopper 30 aswill appear more clearly'hereinafter.

These solids may be added in such proportions.

as to establish an actual particle-size distribution within mass Mm about as follows:

Percent 0-20 microns 20-25 20-60 microns 60-200 microns 30-40 200-400 microns 20-30 400 microns 5 In accordance with the preferred embodiment of the invention, these extraneous solids have cracking activity and may comprise therefore such conventional crackingcatalysts as mixed silicae v t Weight, p 108112 Thru 4 on 10 mesh 5'7 Thru 10 on 20'mesh 19. Thru 20 on 200 mesh 20' Thru 200 mesh 2'.

81 alumina gels, silica-magnesia.composites; or: the like.

A mixture of product vapors and'gases with fluidizing gas, containing about 0.001 to 0.03-lb. of entrained solids per cu. ft. of gasiform material passes overhead from interface. L10 to form a dilute solids-in-gas suspension above level L10. This suspension is passed through line l5 to a system of gas-solids separator, such as cyclones l5, Hand. [8, wherein most of the entrained solids are'sepa'e rated-to be returned to bed M10 through dippipes.

I9, 20, and 2|, respectively. Vapors and. gases now containing merely about 0.001 to 0.004 lb. per cu. ft. of entrained solids fines arewithdrawn throughline 23 and may be passed to a conventional product recovery system (not shown) which preferably includes settling or filtering means for the final removal of entrained solidsfines prior to or during distillation. The fines'so recovered may be discarded, recycled to the retort in a concentrated slurry, or supplied to burner 40, if desired, or used as fuel in other sections of the system. As a result of the low fines carry-over, nodifiiculties arise from slurry formation in the product recovery system.

A carbonized mixture of spent shale andextraneous solids is withidrawn from the bottom of retort I0 through an aerated standpipe 25 at a rate controlled by slide valve 21. If desired, the solids may be stripped of volatileproducts by small amounts of a strippinggas'such as steam which may be introduced through line 2 6 into the annular space surrounding distributing cone 14 in the bottom of retort 10. The withdrawn solids are passed into line 29-wherein they are picked up by a combustion-supporting gas such as air preferably preheated to about 800-1000- F. in heat exchange with process fiue'gases. If desired, a minor portion of the-solids in-standpipe 25, say about'10-40%, may be-passed withv the aid of an inert carrier gas, such assteam;v

through line 32 into the upper portion of the inner combustion section 45-of burner 40. The flow velocity of the gas in line 29 may be maintained as low as about -33 ft. per sec; as a result of the presence of more than 10% 0150-20 microns material. This is an advantagev bee caue higher velocities would cause excessive.at-- trition. The suspension formedin.line- 29. is.

passed through a distributing cone 35 to the lower portion of inner combustion section 45 of burner. 40. Make-up catalyst or other extraneous solid of intermediate particlesize may be supplied from hopper 30 through standpipe 34 -to line.29 and combustion section 45. The amount of oxygen supplied through line 29 should be suflicient to maintain by combustion aburner temperatureabout 50-200 F. higher than the temperature maintained in retort l0.

Particle size control by fines elutriation takes.

As shown in Figplace-in burner as follows. ure 4, burner 40 contains an inner combustion section having a lower. portion 41 of relatively large diameter and an upper portion 49 of rela-. tively small diameter. Combustion section 45is so designed that at the-prevailing gas feed rate a superficial linear gas velocity, substantially below 1.5 ft. per second, preferably between about 0.5 and 1.0 ft. per secondis maintained in the lower portion 41. At this velocity, effectivesegregationof coarse particles within a size range of about 400 to 7,000 microns from particles of less than 400 microns takes place. The coarse material concentrates in the bottom of portion standpipe to be further handled as will appear hereinafter. The finer material concentrates in the upper and middle sections of portion 41 which is provided with a plurality of ports 53 connecting portion 41 with the annular space formed by the Walls of burner 40 and combustion section 45. The particles of less than 400 microns concentrating in the middle section of portion 41 pass through ports 53 into the annular burner space and, in the absence of a supporting fiuidizing gas, drop down to the bottom of burner 40 from which they are withdrawn through standpipe 55 to be further treated as will appear hereinafter. If desired, a small amount of an aerating and/or stripping gas, such as steam or product gas, may be introduced through taps t into the bottom of this annular space in order to remove adhering flue gas and facilitate the flow of the solids, all in a manner known per se.

Particles of less than 400 microns diameter concentrate in the top of portion 4'! and, as a result of the decreasing diameter of portion 4'! and the thus increasing gas velocity, are carried into upper portion 49 of smaller diameter. Portion 49 is so designed that a superficial linear gas velocity of at least 1.5 ft. per second, preferably between about 2.0 and 4.0 ft. per second, is established. At these velocities, at least a major proportion of the fines of 0-20 microns size is fully entrained and carried overhead by the flue gases which may also carry along minor amounts of larger particles in the 20-60 micron range.

The last mentioned relatively dilute suspension which may contain about 0.010 to 0.035 lb. of solids per cu. ft. is withdrawn through line 51 and passed to a primary cyclone separator 59 in which particles larger than 20 microns are separated either to be returned through dip pipe Bl provided with control valve 63 to the middle section of portion 41 of combustion section 40 or to be discarded via line 65 and spent shale accumulator l5. pension flows through line '61 to an additional separating system which may comprise two or more cyclones 69 and and/or electric precipitators H for the substantially complete removal of shale fines which may be collected in accumulator I5 via dip pipes 12, I3, and 14, respectively. Spent shale may be disposed of from accumulator via standpipe 11, preferably after cooling below its ignition temperature of about 300- 500 F.

Returning now to burner 40, the coarse material withdrawn from the bottom of portion 4'! via standpipe 5| may be passed to line 19, suspended therein in a carrier gas, such as air, and passed to the cyclone 69 from which the separated coarse material flows through line 12 to spent shale accumulator 15. The intermediate size particles withdrawn through standpipe 55 are passed at a rate controlled by slide valve 56 to gas line I2 to be suspended therein and passed to retort H! as described above substantially at the temperature of burner 40. The solids circulation rate through line l2 depends on the temperature differential between burner 40 and retort 10. A circulation rate of about 12 to lbs. of hot solids per lb. of fresh shale fed is normally sufficient at the temperature differentials specified above.

It will be appreciated that operation in the manner described permits an effective removal of shale fines and a flexible control of the particle size distribution without any detrimental ef- The remaining solids-in-gas susfect on the retorting, combustion and fiuidization conditions in the retorting and combustion zones and largely independent of the fresh shale feed rate. The particle size segregation and lines removal in heater 40 may be intensified or moderated by a proper control of the superficial linear velocity of the fiuidizing gas without affecting the degree of combustion. The gas velocity may be reduced by supplying smaller amounts of air enriched with oxygen while higher velocities may be established by diluting the air with inert gases, such as steam, flue gases, etc.

In many cases it may be desirable to vary the rate of fines removal without changing the velocity of the fluidizing gas. This may be accomplished by varying the point of fines withdrawal above the dense phase interface. Details of a device particularly suited for this purpose are illustrated in Figure 5 on an enlarged scale.

Referring now to Figure 5 there is shown the top of burner vessel 40 and portions of line 51 for the withdrawal of the shale fines suspended in the fiue gases as described with reference to Figure 4. Line 51 has the form of a sliding pipe section which is slidably supported in a cover plate 4| of burner 40 by means of a stufiing box 90. A second stuffing box 02 supports pipe section 5'! slidably in a stationary pipe section 51a. A rack 94 attached to pipe section 51 cooperates with a pinion 96 for the adjustment of the distance over which pipe section 5! penetrates into burner 40. Pinion 06 is preferably operated by remote control. The rate of fines removal may be increased or decreased by lowering or raising pipe section 57 so that the distance between its intake end and the interface of the fluidized bed in heater 40 will be decreased or increased. The more closely the intake end of pipe section 51 approaches the interface the higher will be the rate of fines removal and vice verse, at any given flow velocity of the fluidizing gas.

While stufling boxes and a rack and pinion arrangement have been shown in Figure 5 for the purpose of lifting and dropping the intake end of pipe section 51, it will be understood that any mechanical equivalents of these means may be used. These and other modifications of the systems illustrated in the drawing will appear to those skilled in the art without deviating from the spirit of the invention.

The invention will be further illustrated by the following specific example.

Example A system of the type illustrated in Figure 4 may be operated, for example, at the conditions tabulated below.

Retort:

Temperature, F c Residence Time, mins 5 Inventory, tons 100 Density, cu. ft 30 Diameter, ft 20.5 Bed height, ft 20 Bed velocity, ft./sec 1.2

Fluidizing gas s. c. f. in. (tail gas,

steam, etc.) 22,500 Pressure, p. s. i. g 15 Carryover, lb./cu. ft 0.003 (thru cyclones) tons/hr 3 11 12 Burner; which comprises passing a gas upwardly .in're.

.Percent carbon .on freshly retorted lowerportion of said combustion zone-at a:supershale entering burner 13.2 ficial linear velocity of substantially lessthan Ozrequirementss. c...f...m 3,280 1.5.ft. per .second whereby segregation of;coarse Air rate, s. c. f..ll'1. (2% eXcess-.O2). 17,300 6 particles .having a diameter of about 400 to Velocity in enlarged section, ft./sec 0.7 7,000 microns from particles less than 400 microns Velocityin small section,.ft.sec 3.5 in diameter takes place in said lower portion, Diameter, .ft. increasing .said velocity thereafter in an upper Enlarged section 42 portion :of said combustion zone substantially .Small section .19 it) above 1.5 ft. vper .second whereby solids fines of :Burner .temperature, F 1,020 -'-20 microns ,particle size are fully entrained Pressure, p. s. i. g and removedoverhead from said combustion: zone Density, lbs./ cu. ft. ito-forma fluidized mass of intermediate particles .Enlarged section -40 lessthan 400 microns butmore than 20 microns .Small section 20 15 .in diameter above ;said fluidized coarse par- Bedheight, ft.- .ticles, returning at least a major portion of said Enlarged section 15 ,segregatedintermediate. size particles .to 'saididis- Small section '5 .tillation. zone for the purposeof heat;supply,: and .Inventory,.tons 1435 withdrawing .said :coarse particles downwardly Residence, mins 4 from said combusion zone. Carry-over- 12. .The processzof claiml inwhichextraneous lb./cu, it 0- 3 rnondisintegratin solids having a particle size Tons/hr .55 of about ,60--200.microns are added ;to said .cir- Steam orinert gas rate, s. c. f..m 10,000 'culating solids3inamountsradequate 'to establish Circulation and feed: a concentration of about 25 ito 50% of said Feed, tons/hr 100 .60-200rniicrons sizezsolids in saiddistillation'and Oil content of feed, gals/ton combustionizones. Carbon content of feed, percent by :3. The processof claim 2iin which said 'exweight 12.2 traneoussolidshave cracking activity. Circulation, tons/min 20 3O 4. The .processof claim 1 in'which the'rate of Inert diluent addition rate, tons/day '5 fines removalfrom said comhustion'zoneis con- Coarse spent shale withdrawn from trolled by'varying the. level of the 'pointoffines burner, tons/hr 137 removal .above tthe interface of said .fiuidized solids insaid combustion zone.

.5. The "process :of claim .1 in .which spent solids circulating'from said distillation zone .to said combustion zone :are supplied to saidicom- At these conditions, the particle "size distribution in the various sections of the system may "be as 'follows:

Percent by Wirrht of Size .bustion zone at .,a point not substantially below rtan 'emiiens the upperlevel :of .the :fiuidized isolids inasaid 40 combustion zone. ,pe id sizes 0-20 ,zo.-e0 0-200 .zooezooo 'D B f laiml iIl'WhiCh freshcarbonaceous solids-are supplied Lto'said distillation Burner: zoneat a'point not'substantially below the upper 65 25 2 0 level of the fluidizedimass in said distillation v15 10 5. 7o Top of Bed 3o 20. 40 10 Z0119- Central' Circulating)'Bed 20 10 45 25 gt} Top JAMES' WJCARR, JR. ggg LINDSAY I. GRIFFIN, 'JR. Feed 2' (EDWARD W. S. NICHOLSON.

The foregoing description and exemplary oper References Cited in :the :file ."Of'thlS patent ations have served to illustrate preferred -em- U ITED STATES PATENTS bodiments of the invention but are not intended Number Name Date to be limi n n Scope 2,387,684 .Scheineman Dec. 28, 1943 What is claimed is: I 2,353,505 .Scheineman July 11, 1944 1. In the distillation of carbonaceous solids of 2,396,709 ,Lefier a 19, 45

the type of oil shale which disintegrate during 2,399,050 .Martin Apr. 23, 1946 distillation whereinthesubdividedrsolidsare dis- 2,480,670 .Peck u ,.30, 1949 tilled inthe form ofa dense turbulent mass'fiuicli2,483,485 .Barr Oct. 4,1949

ized by an upwardly flowing gasiform medium in 2,548,026 Kaasa Apr. .10, 1951 a distillation zone, spent solids are subjected to combustion and highly heated in the fluidized FOREIGN PATENTS state in a combustion zone and 'heatxistsupplied Number Country Date to said distillation zone in the form of sensible v 573,711 Great'Blitain Y' 94 heat of solids circulating from'said combustion 536,391 Great'Britain M 1947 :zone to said distillation zone, the improvement 3 Great Br a p 6, 19 8 

1. IN THE DISTILLATION OF CARBONACEOUS SOLIDS OF THE TYPE OF OIL SHALE WHICH DISINTEGRATE DURING DISTILLATION WHEREIN THE SUBDIVIDED SOLIDS ARE DISTILLED IN THE FORM OF A DENSE TURBULENT MASS FLUIDIZED BY AN UPWARDLY FLOWING GASIFORM MEDIUM IN A DISTILLATION ZONE, SPENT SOLIDS ARE SUBJECTED TO COMBUSTION AND HIGHLY HEATED IN THE FLUIDIZED STATE IN A COMBUSTION ZONE AND HEAT IS SUPPLIED TO SAID DISTILLATION ZONE IN THE FORM OF SENSIBLE HEAT OF SOLIDS CIRCULATING FROM SAID COMBUSTION ZONE TO SAID DISTILLATION ZONE, THE IMPROVEMENT WHICH COMPRISES PASSING A GAS UPWARDLY IN A LOWER PORTION OF SAID COMBUSTION ZONE AT A SUPERFICIAL LINEAR VELOCITY OF SUBSTANTIALLY LESS THAN 1.5 FT. PER SECOND WHEREBY SEGREGATION OF COARSE PARTICLES HAVING A DIAMETER OF ABOUT 400 TO 7,000 MICRONS FROM PARTICLES LESS THAN 400 MICRONS IN DIAMETER TAKES PLACE IN SAID LOWER PORTION, INCREASING SAID VELOCITY THEREAFTER IN AN UPPER PORTION OF SAID COMBUSTION ZONE SUBSTANTIALLY ABOVE 1.5 FT. PER SECOND WHEREBY SOLIDS FINES OF 0-20 MICRONS PARTICLE SIZE ARE FULLY ENTRAINED AND REMOVED OVERHEAD FROM SAID COMBUSTION ZONE 